Safety control apparatus for fuel burners



9, 1945. s. e. ESKIN ET AL 2,366,774

' SAFETY CONTROL APPARATUS FOR FUEL BURNERS Filed April 15, 1942 INVENTOR. CHARLES K.6TR0BE1..

AND

BY SAMUEL 6. Es uv.

- M ATTORNE).

Patented Jan. 9, 1945 UNITED STATE S PATENT OFFICE SAFETY CONTROL APPARATUS FOR FUEL BURNERS of Pennsylvania Application April 15, 1942, Serial No. 439,148

12 Claims.

This invention relates to control devices and, more particularly, to electrically operated safety controls.

A safety control device constructed in accordance with this invention may be used in conjunction with heat or flame sensitive elements in a safety pilot to permit supply of fuel to a main burner or to shut off the fuel supply when the pilot burner is extinguished. It may also find a field of usefulness in installations where a pilot burner is not used and the safety control operates directly in response to the condition of the main burner. In all such arrangements the flame sensitive element is connected in circuit with the solenoid valve which controls the fuel supply to the main burner and is exposed to the flame of the main or pilot burners. In the arrangement to which this invention pertains, the flame sensitive element has a positive temperature coefficient of resistance and when unheated will permit insufficient current to flow to the solenoid valve to retain it in open position.

In order to provide quick shut-off of the solenoid valve when the flame is extinguished and the flame sensitive element cools, the circuit constants are adjusted to provide an operating current for the solenoid valve which is only slightly above the minimum required to hold the valve open when the flame is burning. As the line voltage at utilization outlets varies considerably in different localities and at different times in the same locality, the circuit constants are adjusted at the lowest line voltage which experience has shown is likely to occur. It will be apparent that in the higher voltage ranges the shut-off time will be longer than that in the lower ranges unless special equipment, such as a constant current transformer, is used. In domestic heating appliances where expense is an important consideration and special equipment prohibited for this reason it is none the less desirable that the operating valve current should be maintained only slightly above the release value over any usual range of line voltages which may be encountered. Otherwise, the release time of the solenoid valve would necessarily follow the line voltage variation and would permit the escape of unburned fuel in undesirable quantities under the higher line voltage conditions.

It is an object of this invention to reduce the operating time of a safety device to a minimum upon the establishment of conditions it is desired to control.

Another object of the invention is to render the device substantially uniform as to operating time over a range of operating conditions.

Another object of this invention is to achieve the results sought without adding materially to the cost of manufacture or departing from simple and reliable construction of parts.

Other objects and advantages will become apparent from the following description taken in connection with the accompanying drawing, wherein is shown a, schematic view of a safety control device for a gaseous fuel burner embodying the invention.

Referring more particularly to the drawing, a gaseous fuel burner l0 and an associated pilot burner H are shown as being supplied with fuel by a main fuel pipe I. The fuel supply to both burners is controlled by a main valve l8 which may be either manually or thermostatically operated. Interposed in the fuel supply pipe l4 between the main valve l6 and the burner ill is an electromagnetic or solenoid gas valve 18 of any knowntypehavinga movable valve member which may be arranged, as in this instance, to be opened when suflicient energizing current is applied to the solenoid and to be closed by gravity or other bias when such current is reduced below a certain minimum value. Operation of the main control valve Hi from closed to open position will per- .mit flow of fuel from the pipe It to the pilot burner l2 but fuel is not supplied to the main burner Ill unless the solenoid valve I8 is also in open position.

Electric current for the operation of the apparatus is supplied by the line wires 20 connected to the primary of a transformer 22 which, in this instance receives commercial current at the primary where a voltage variation from IDS-I25 volts can occur. The secondary of the transformer 22 delivers the current at voltages varying in accordance with the primary voltage variations above and below an average of six volts and is connected by a wire 24 to one terminal of a main switch which, in this instance, is incorporated in the main valve l6. Any suitable means may be used to close the switch when the main valve I6 is actuated to open position. The other terminal of the main switch of the valve I6 is connected by a wire 26 to one end of a flame sensitive element 28 positioned adjacent the pilot burner 12 and exposed to the flame thereof. The flame sensitive element 28 may be in the form of a coil of wire formed from ma.- terial having normally a relatively low resistance and a positive temperature coefllcient of resistance forming a ballast resistor. It will be apparent that other types of flame sensitive, heat responsive or thermal resistanceelements having the required characteristics may be substituted.

The other end of the flame sensitive element 28 is connected by a wire 30 with one end of a parallel mesh included in the secondary circuit, the other end of this parallel mesh being connected by a wire 32 to the other terminal of the secondary of the transformer 22. One branch of the parallel mesh comprises a resistance element 34 which will be hereinafter designated as a valve control resistor. This resistor 34 may, as in the case of the resistor 28, be in the form of a coil of wire of material having normally a relatively low resistance and a positive temperature coefficient of resistance forming a ballast resistor.

'The resistor 34 is not, however, exposed to any flame but is adapted to become heated upon passage of electric current therethrough and will change its resistance in accordance with changes of temperature.

The other branch of the parallel mesh comprises a constant resistance element 36 and a manually operated switch 38 in series therewith. The switch 38 is normally open but is adapted to be closed to establish the circuit through the parallel mesh. The solenoid valve [8 is connected in parallel circuit with the flame sensitive element 28 by means of a wire 40 connecting one terminal thereof with the wire 26 and another wire 42 connecting the other terminal thereof with the wire 30. A fuse, preferably of the slowacting bimetallic snap-switch type, designated by the numeral 44 may be interposed in the wire 46 for protecting the solenoid valve coil in the event that an open circuit occurs in the flame sensitive element 28.

In the operation of the device the manual or thermostatic closing of the main switch of valve i6 is effected upon opening of this valve as described and permits fuel to flow to the pilot burner [2. As the solenoid valve l8 remains closed, no fuel can flow to the main burner H1 at this time. The secondary circuit may be traced from one terminal of the transformer 22, wires 24 and 28 through the main switch of valve it, the wires 40 and 42 through the coil of the solenoid valve l8, wire 30 to the valve control resistor 34 and wire 32 to the other terminal of the secondary of the transformer 22. Current also flows through the shunt established by the flame sensitive element 28 around the coil of the solenoid valve l8 causing this element to become heated to some extent. The current values in the secondary circuit are adjusted so that the combined resistances of the flame sensitive element 28 and the valve control resistor 34 permit insufficient current to flow to the coil of the solenoid valve ill to actuate this valve to open position.

The fuel issuing from the pilot burner l2 may be ignited by e. match or other suitable means and additional heating of the flame sensitive element 2i? will then occur. After a period of time has elapsed for the flame sensitive element 28 to become heated to a temperature sufficient for a purpose apparent hereinafter, which should be about one minute, the manually operated switch is closed and the circuit of the parallel mesh is completed. The combined resistance of the constant resistance 36 and the valve control resistor 3a in parallel circuit is sufficiently smaller than the resistance of the resistor 34 alone so that the secondary current is now of a value at which enough current will flow to the coil of the solenoid valve to actuate the valve to open position. It should be noted that such actuation can occur regardless of whether the flame sensitive element 23 is heated by the burner flame. After the few seconds have elapsed during which the solenoid valve l8 has been actuated to open position, the manually operated switch 38 may be released to open position thus removing the shunt established by the constant resistance 36 and leaving only the branch of the parallel mesh comprising resistor 34 in the secondary circuit.

It will be apparent that the flame sensitive element 28 and the coil of the solenoid valve H! are in parallel circuit and this combination is in series circuit with the valve control resistor 34 and the transformer secondary. The resistance of this parallel circuit is increased sufficiently by the higher resistance value of the flame sensitive element 28 when heated, as previously described, to permit sufficient current to continue to flow to the coil of the solenoid valve Hi to maintain it in open position. The circuit constants are adjusted at the lowest line voltage, which may be volts at the primary, and the normal, steady operating current is only slightly above the minimum value required to hold the valve in its open or operating position.

When the flame sensitive element 28 cools, as by extinguishment of the pilot burner flame, its resistance is decreased with a resultant decrease in the current through the coil of the solenoid valve l8. Such effect follows from the increase in total secondary current which causes an increase in the voltage drop across the valve control resistor 34. The increase across the resistor 34 causes a decrease in voltage drop across the coil of the solenoid valve 18. Since the voltage drop across the coil of the solenoid valve is is decreased, the current for holding the valve in the open positio is decreased sufficiently to cause the valve to close if the circuit constants are chosen with this end in view.

It will be apparent that by making the valve control resistor 34 sensitive to current changes the decrease in voltage drop across the coil of the solenoid valve I 8 will be accelerated whenever an increase in resistance of the valve control resistor 34 occurs. This effect is due to an increase in the current through the valve control resistor 34 when the flame sensitive element 28 cools and its resistance becomes lower. The resultant temperature rise of the valve control resistor 34 causes an increase in voltage drop across this element and a rapid decrease in voltage drop across the solenoid valve l8.

The adjustment of the circuit constants to provide an operating currentonly slightly larger than the current required to hold the solenoid valve [8 open causes the current through the valve to be reduced below release value in a minimum time at the lowest line voltage. However, by providing the current sensitive valve control resistor 34 this effect is achieved at any of the varying line voltages which ordinarily may be expected. Thus, when the line voltage rises the secondary current increases, but the resistance of the valve control resistor 34 creases due to the larger current tendency for the secondary current .icrease with an increase in line voltage is counteracted by the increase in resistance of the secondary circuit due to the action of the current sensitive valve control resistor 3%. Consequently, the release time of the solenoid valve I8 is maintained uniformly small over the usual range of line voltage variation.

The device will operate safely if the switch 38 is manually closed when there is no fuel in the main fuel pipe 54. The closing of this switch will cause the solenoid valve ill to be actuated to open position as described. When the manual pressure is released and switch 38 opened while the flame sensitive element 28 remains unheated,

the solenoid valve I8 returns to its closed position.

While the invention has been described in connection with a safety control device for a safety pilot, it will be understood that when desired the pilot burner could be dispensed with and the safety control operate directly on the main burner. The solenoid valve l8 could also control the fuel supply to both the pilot burner and the main burner in cases where a complete shut-off of fuel to both burners is desired upon closing of the solenoid valve. In the latter case, the flame sensitive element 28 would be positioned adjacent either the pilot or main burner and the solenoid valve l8 would control the fuel'supply to both burners instead of only the main burner supply. The starting operation would vary only insofar as operation of the main switch I6 would not permit fuel to flow to either burner. Hence, in order to light a burner with a match the switch 38 would be manually closed and held closed for about one minute until the solenoid valve l8 would remain open upon release of the switch to open position.

It will be understood further that the invention is not limited to the use of a flame operated element as other means for changing the temperature of such a device could be substituted. The solenoid valve could be replaced by a relay to control many types of electrically operated devices and is not limited to the control of fuel supply to a gaseous fuel burner.

Considerable flexibility of circuit arrangement .results from the use of the electrically operated safety control described and shown herein, as it will be apparent that the value of the respective resistances may be varied to suit various operating conditions. Moreover, while the preferred form and arrangement of parts has been illustrated and described, it will be apparent that the control is not limited to this particular embodimeni; but various changes may be made within the scope of the following claims.

We claim:

1. A control device comprising in combination, a transformer having its primary energized from a source of current supply subject to voltage variations, means in circuit with the secondary of said transformer movable between positions for establishing a condition, electrical resistance means adapted to vary in resistance in response to variations in the current values in said circuit, said resistance means maintaining the current supply to said condition establishing means substantially constant over the range of primary voltage variations, means operable in conjunction with said resistance means for temporarily varying the resistance to current flow in said circuit and causing said condition establishing means to be moved to one position, and means electrically connected with said condition establishing means and responsive to the condition established thereby for cooperating with said resistance means subsequent to said operable means for varying the supply of current to said condition establishing means in accordance with said condition.

2. A control device comprising in combination, a transformer havin its primary energized from a source of current supply subject to voltage variations, means in circuit with the secondary of said transformer movable between positions for establishing a condition, electrical resistance means adapted to vary in resistance in response to variations in the current values in said circuit, said resistance means maintaining the current supplyto said condition establishing means substantially constant over the range of primary voltage variations, means operable in conjunction with said resistance means for temporarily varying the resistance to current flow in said circuit and causing said condition establishing means to be moved to one position, and a second electrical resistance means adapted to vary in resistance in response to the condition established by said condition establishing means for cooperating with the first said resistance subsequent to said operable means for varying the supply of current to said condition establishing means in accordance with said condition.

3. A control device for a burner comprising in combination, a transformer having its primary energized from a source of current supply subject to voltage variations, means in circuit with the secondary of said transformer movable between positions for controlling the condition of the burner, electrical resistance means adapted to vary in resistance in response to variations in the current values in said circuit, said resistance means maintaining the current supply to said controlling means substantially constant over the range of primary voltage variations, means operable in conjunction with said resistance means for temporarily varying the resistance to current flow in said circuit and causing said condition establishing means to be moved to one position, and means subject to the heat of the burner and electrically connected with said controlling means for cooperating with said resistance means subsequent to said operable means for varying the supply of current to said controlling means in accordance with the condition of the burner.

4. A safety control device comprising in combination, a transformer having its primary energized from a source of current supply subject to voltage variations, electrically operated means in circuit with the secondary of said transformer and movable between positions for controlling a condition, the operating current in said circuit at the lowest voltage supplied being substantially the minimum value required to maintain said controlling means in operating position, a varying electrical resistance element in circuit with said controlling means for maintaining the current supply to said controlling means substantially constant over the range of primary voltage variations, whereby the operating current for said controlling means is maintained substantially at said minimum value, and means establishing a shunt for said controlling means responsive to said condition for determining whether the operating current therefor is maintained at said minimum value.

5. A safety control device comprising in combination, a transformer having its primary energized from a source of current supply subject to voltage variations, electrically operated means in circuit with the secondary of said transformer and movable between positions for controlling the condition of a burner, the operating current in said circuit at the lowest voltage supplied being substantially the minimum value required to maintain said controlling means in operating position, a varying electrical resistance element in circuit with said controlling means for maintaining the current supply to said controlling means substantially constant over the range of primary voltage variations, whereby the operating current for said controlling means is maintained substantially at said minimum value, and a varying electrical resistance element subject to the heat of the burner and connected in parallel circuit with said controlling means, said last named element decreasing its resistance when unheated and thereby decreasing the operating current for said controlling means below said minimum value.

6. A safety control for gaseous fuel burners having main and pilot burners and means for supplying fuel thereto, comprising in combination, a transformer having its primary energized from a source of current supply subject to voltage variations, an electromagnetic means in circuit with the secondary of said transformer for controlling fuel supply to the main burner, the operating current in said circuit at the lowest voltage supplied being substantially the minimum value required to maintain said controlling means in operating position, a varying electrical resistance element in circuit with said controlling means for maintaining the current supply thereto substantially constant over the range of primary voltage variations, whereby the operating current for said controlling means is maintained substantially at said minimum value, and a thermal resistance element subject to the heat of the pilot burner and connected in parallel circuit with said controlling means, said thermal element having suihcient resistance when unheated to de crease the operating current for said controlling means below said minimum value.

7. A safety control for gaseous fuel burners having main and pilot burners and means for supplying fuel thereto, comprising in combination, an electromagnetic valve movable between positions for controlling the fuel supply to the main burner, an energizing circuit for said valve, a varying resistance element in said circuit responsive to the current values, a thermal resistance element subject to the heat of the pilot burner and connected in parallel circuit with said valve, the combined resistance value of said elements providing only sufficient current for holding said valve in position to supply fuel to the main burner when the thermal element is heated but insuflicient current to actuate said valve to said position, and means operable upon said thermal element becoming heated by the pilot burner for temporarily reducing said resistance value to permit actuation of said valve.

8. In a safety control device, a source of electrical energy, electrically operated means movable between positions for controlling a condition, a resistance element adapted to vary in resistance in response to variations in current values in circuit with said controlling means, means operable in conjunction with said resistance element for temporarily varying the resistance to current flow in said circuit and causing said controlling means to be actuated to one controlling position, and a second resistance element adapted to vary in resistance in response to variations in said condition and being cooperable with the first said element subsequent to said operable means to vary the resistance in said circuit, said variation causing said controlling means to be maintained in said position under one condition and actuated to another controlling position under another condition.

9. In a safet control device, a source of electrical energy, electrically operable means movable between positions for controlling a condition, a resistance element adapted to vary in resistance in response to variations in current values incircuit with said controlling means, I

means operable in conjunction with said resistance element for temporarily decreasing the resistance to current flow in said circuit and causing said controlling means to be actuat d to one controlling position, and a second resistance element adapted to vary in resistance in response to variations in said condition and being connected with said controlling means and first said element, the combined resistance value of said elements providing suflicient current for causing said controllin means to be maintained in said position under one condition and insuflicient current under another condition.

10. In combination, an electromagnet having a member movable between positions for controlling a condition and biased to one of said positions, a source of electrical energy, a resistance element adapted to vary in resistance in response to variations in current values, said element being connected in series circuit with said electromagnet, switch means adapted when closed for cooperation with said element for temporarily de creasing the resistance to current flow in said circuit and causing said member to move to the other of said positions, and a second resistance element adapted to vary in resistance in response to variations in said condition, said elements cooperating to vary the resistance in said circuit when said switch is opened causing said member to be retained in said other position against said bias under one condition and to move to biased position under another condition.

11. In a safety control device, a source of electrical energy, electrically operated means movable between positions for controlling a condition, a varying electrical resistance element in circuit with said controlling means, an auxiliary resistance element for temporarily shuntin the first said element, the combined resistance of said elements having a value such that said controlling means is actuated to one position, and means responsive to said condition and shunting said controlling means, said condition responsive means in one condition having a resistance value such that said controlling means is maintained in said position upon removal of the shunt established by said auxiliary resistance element and in another condition causing movement of said controlling means to another position.

12. In a safety control device, a source of electrical energy, electrically operated means movable between positions for controlling a condition, a varying electrical resistance element in circuit with said controlling means, an auxiliary resistance element for shunting the first said element, a switch for connectin and is n ting said auxiliary element in said shunt, the combined resistance of said elements when so connected having a value such that said controlling means is actuated to one position, and means responsive to said condition and shunting said controlling means, said condition responsive means in one condition having a resistance value such that said controlling means is maintained in said position upon operation of said switch to disconnect the shunt established by said auxiliary resistance element and in another condition caus ing movement of'said controllin means to another position.

SAMUEL G. ESKIN. CHARLES K. STROBEL. 

